US President George Bush knows he has some fences to mend on this side of the Atlantic. His trip to Ireland, Britain and other EU countries in the coming months is seens as part of a "charm offensive" by the Bush regime.

Increasing unease among his European allies over his "axis of terror" campaign has seen a growing number of EU politicians including EU External Commissioner Chris Patten criticise the apparent rush to attack other states known to be soft on terrorism.

Few now doubt that the Bush administration is preparing to attack Saddam Hussein's Iraq, most likely this summer or autumn. While Ireland and the other EU states were prepared to stand beside the US in the campaign again Taliban backed terrorists in Afghanistan the pace of the American build up for a series of armed engagements elsewhere is beginning to cause concern in some European capitals.

Differences and divisions between the United States and European nations in the aftermath of conflict are hardly unusual. They occurred after both world wars. But there is a distinctive feature to the present pattern of disagreement. In the past, it was always the United States which, to prominent Europeans, seemed to want to declare an end to battle prematurely and then impose some idealistic concept of international relations (the League of Nations, the United Nations).

This time, the roles are reversed. The EU is desperately seeking to dissuade President Bush from extending the war on terrorism while insisting that he should revert instead to a "multilateralist" foreign policy. Hence the accusations of US arrogance, ignorance and unilateralism.

The demand for American multilateralism, and the condemnation of unilateralism, fails to recognise the nature of global politics. People and countries might shape systems, but systems shape countries and people. It is impossible to divorce the exercise of power from the context in which it is set.

The United States is today, ironically courtesy of Osama bin Laden, neither a superpower nor, as the French have observed, a hyperpower, but a megapower without historic precedent. The extent to which the United States dominates the various conventional facets of power - military, economic, technological, cultural and political - far outstrips anything achieved by the British, French or Spanish empires. The only theatre of power which has been contested before, and where the United States holds little influence, is religion. That fact may shed valuable light on contemporary events and circumstances.

A singularly unipolar political structure will produce, absolutely inevitably, a unilateralist outcome. After all, a commercial sector in which one company holds an 85 per cent market share will logically be dominated by that corporation. European states, whether alone or forced together in an artificial construction in the hope of "pooling," rather than diluting, their resources, are insignificant by comparison.

Genuine multilateralism requires a multipolar order. That can only be achieved when authority is distributed evenly across a number of players (a transient event in human history so far) or if the largest power chooses, for some reason, to shrink itself to meet the occasion. That was the essence of American foreign policy in the decade between the Gulf War and September 11. George Bush Sr was distracted by recession while Bill Clinton felt personally incapable of flexing the biceps of the American body politic. It was an embarrassing episode which created the climate that allowed al-Qaeda to be born and to flourish.

Circumstances have allowed the present President to escape that trap and embrace the real new world order. His successors are unlikely to wander back into the Clinton quagmire. American "unilateralism" can wear conservative or liberal clothes, but it will be the power-suit for decades.

There are two extraordinary facets of American authority that merit serious consideration. The first is that the United States is the only such nation in history whose expansion has been based on drawing citizens into its borders rather than pushing out its boundaries to conscript others involuntarily within them.

Immigration into the United States is accelerating.

Half a century ago America resembled a sort of United States of Europeans, constituting, on the whole, those attracted from Ireland, Germany, Italy, Poland, Russia and Britain while African-Americans were basically second-class citizens.

This in turn largely explains why American politicians in the 1940s were sympathetic to European integration and could not really comprehend why the British were so hostile to it.

The waves of both Hispanic and Asian immigration that have occurred since then, plus the civil rights movement, have rendered the United States more cosmopolitan. In one sense, therefore, the call for a world order based on the United Nations is superfluous. We have, via the United States, found one.

If this is, as critics contend, "imperialism," then it has an extremely liberated character.

The second point is that the sole viable alternative to unilaterism is not multilateralism, but isolationism.

Although almost all American politicians feel obliged to deliver speeches proclaiming that "isolationism is not an option," the US could, to a considerable extent, opt out of the international arena and wallow instead in affluent splendour. It is still a self-sufficient economy and there is no threat of invasion.

None of the traditional empires were ever in the position to stand still, or sit matters out: their rivals would, as they did, exploit such inactivity to their advantage.

If European politicians dislike American unilateralism, therefore, they should ponder the alternative.

It would be an international order in which the United States rested, to borrow from Ronald Reagan, as "a shining city on a hill" while anarchy reigned supreme in the valleys.

We have had at least one period of history with no dominant power at all - let alone a benign, democratic, one. It is known, quite rightly, as the Dark Ages.

The Times, London

- Tim Hames